Id ‘Safari2’ has already been specified and must be unique

After updating with Service Pack 1 or using PSConfigUI pointing the browser to a site collection you can encounter the well known “yellow page of death” with this error.

In the root directory of the web application (C:\inetpub\wwwroot\wss\VirtualDirectories\<port number>) there is the AppBrowsers directory , where normally there are 2 files compat.browser and compat.moss.browser

An update can create an backup file , in my case i have found compat – Copy.browser and there is an issue that you cannot have two similar files named with .browser extension: i have renamed as compat – Copy.browser.old and the problem is resolved.